The use of so-called safety glazing or penetration resistant glazing for windows, windshields and the like using multiple layers of polycarbonate, glass, and other resinous materials is well known. For example, glass polycarbonate resin laminates are described in U.S. Pat. No. 3,666,614, the glass and polycarbonate being cohered together using an ethylene-vinyl copolymer. In U.S. Pat. No. 3,520,768, there are described laminates of relatively thick glass having a comparatively thin polycarbonate foil as the cohering material. It is also known, as described in U.S. Pat. No. 4,027,072, to utilize certain polysiloxane-polycarbonate block copolymers as an adhesive in preparing polycarbonate containing laminates. While generally useful, these laminates suffer from an inability to withstand multiple shots, especially when struck by high velocity bullets, such as those fired from rifles. Thus, for example, in prior art laminates utilizing thick forward facing (impact receiving) glass plies, multiple shots at the thick glass front ply cause much glass cracking and removal of glass from the laminated structure making it vulnerable to repeat hits. In order to withstand multiple high velocity bullet strikes, especially high velocity rifle bullets, the heretofore known laminates had to be extremely thick and heavy. Even these thick and heavy laminates were not entirely successful since spalling on the back or downstream face of said laminates occurred with the resultant danger of injury due to this spalling to persons behind these laminates. Thus, there is a need for laminates which are relatively thin, are lightweight, and are able to withstand repeated hits by high velocity bullets.
The present invention provides a laminate structure which has relatively light weight, is relatively thin, and yet is capable of withstanding repeated high velocity bullet strikes without bullet penetration or spalling of the back or downstream layer.